1. Technical Field of the Invention
The present invention relates to a document feeding apparatus for use in a copying machine, image reader, microphotographing apparatus or the like wherein documents stacked in a document stack tray are automatically fed one by one to a platen where an image is exposed and read or photographed and then discharged automatically, and more particularly, to a document feeding apparatus in which two sheets of originals are once aligned both in front and in the rear of a pair of rollers provided in an intermediate portion of document transport path and then the sheets are automatically transported under subsequent handling mode (hereinafter referred to as two-in-one handling mode) as if they are one sheet of original and are discharged automatically.
2. Description of Related Art
The two-in-one handling mode as described above is simply accomplished by a transport mechanism which includes a downstream side transport means a on the intermediate portion of the transport path, a pair of rollers d, an upstream side transport means e, a first driving source b and a second driving source f. The downstream side transport means a is connected directly to the first driving source b, while the pair of rollers are connected to the first driving source b through a clutch c. The upstream side transport means e is connected directly to the second driving source f. An operation in a conventional method has been processed in a manner which will be described below.
Firstly, the first and second driving sources b, f and the clutch c are turned on to transport a first original OD1. When the trailing end of the first original OD1 has passed through the pair of rollers d, the clutch c and the second driving source f are turned off while the first driving source b is turned on to transport the first original OD1 reversely to the pair of rollers d to adjust the rear edge of the first original OD1 at the nip portion of the rollers. Then, the first driving source b is turned off to stop the downstream side transport means and on the other hand, the second driving source f is turned on to transport a next original OD2 to the pair of rollers d so that the leading edge of the next original OD2 is adjusted at the nip section of the pair of rollers d.
In such a manner, the first original OD 1 and the next original OD2 can be sequentially aligned in front and in the rear of the pair of rollers d as illustrated in this figure. Under the state, each of the first and second driving sources b, f are simultaneously turned on while the clutch c is also turned on to drive the upstream side transport means e, the pair of rollers d and the downstream side transport means a so that the first original OD1 and the next original OD2 are transported in alignment, for instance, onto a platen glass g for copying operation.
On the other hand, the originals OD1 and OD2 sent for copying operation on the platen glass g are discharged by a downstream side transport means h onto an original discharge tray k as shown in FIG. 2. In the discharging operation, a controller confirms the completion of original discharging action by detecting the rear edge of an original being discharged onto the discharge tray k by an original detecting sensor.
In the two-in-one handling mode, originals are often discharged on the original discharge tray with unregistered manner because the rear edge of the original OD1 discharged firstly is pushed out by the leading edge of the original OD2 being subsequently discharged. In order to improve the registration, it is necessary to raise the transport speed of a discharge means a little higher than that of the downstream side transport means a to keep apart the distance between the first original OD1 and the next original OD2. But, in case the distance between the first original OD1 and the next original OD2 exists, the sensor f detects not only the rear edge of the original OD2 but also the rear edge of the original OD1. Therefore, the controller can not confirm the completion of original discharge action exactly by the original detecting sensor.